1. Field of the Invention
This invention concerns a spin-valve magnetoresistance sensor in which a free-side magnetic layer, nonmagnetic layer, and fixed-side magnetic layer are formed by layering on a substrate, and in which the magnetization of the fixed-side magnetic layer is fixed by an antiferromagnetic layer. In particular, it concerns a so-called synthetic type spin-valve magnetoresistance sensor in which multiple ferromagnetic films are formed by layering with fixed-side magnetic films enclosing a nonmagnetic coupling film, and a thin film magnetic head provided with this magnetoresistance sensor.
2. Background Information
In the past, in order to obtain a high magnetic field sensitivity from magnetic heads used for reproduction, magnetoresistance (MR) sensors with a spin-valve film structure exhibiting a giant magnetoresistance effect have been developed. In general, spin-valve MR films have a sandwich structure in which two opposing magnetic layers with an intervening nonmagnetic layer are formed by layering on a substrate. Whereas the fixed-side (pinned) magnetic layer has its magnetization fixed parallel to the signal magnetic field by the exchange-coupling magnetic field with the neighboring antiferromagnetic layer, the magnetization of the free-side (free) magnetic layer comprises a single magnetic domain through a hard-bias method utilizing the magnetic field of a permanent magnet, and so can be rotated freely by an external magnetic field.
When the magnetization of the free magnetic layer rotates due to the external magnetic field from magnetic recording media or other source, the angular difference in the directions of the magnetizations appearing in the two magnetic layers causes a change in the magnetoresistance of the MR film, which enables the signal recorded in the recording media to be detected. A spin-valve film is ideal when used in a state in which the magnetization direction of the pinned magnetic layer and the magnetization direction of the free magnetic layer are orthogonal, since good linear response with a broad dynamic range is then obtained. However, the pinned magnetic layer, as a single layer, has a magnetic moment, and the magnetostatic action of the latter may in some cases affect the free magnetic layer such that the magnetization direction is no longer uniform. Consequently part of the MR sensor is quickly saturated under a signal magnetic field, there is concern that the symmetry of the sensor output might be impaired, and the dynamic range might be limited.
Hence recently, as for example has been disclosed in laid-open patent application Hei7-169026 and elsewhere, a synthetic spin-valve MR sensor has been proposed which uses, in place of the single layer of the prior art, a multi-layer structure pinned magnetic layer in which two ferromagnetic films are formed by layering to enclose a ruthenium (Ru) or other nonmagnetic coupling film. In this pinned magnetic layer, the two ferromagnetic films have their magnetizations in anti-parallel orientation and are strongly antiferromagnetically coupled, and moreover the magnetic moments of the two ferromagnetic films cancel each other. In this way the adverse influence on the free magnetic layer of the magnetostatic action is eliminated or reduced, the sensor sensitivity is raised, and higher recording densities can be employed in magnetic recording.
In the synthetic-type spin-valve MR sensor described above, spin-dependent electron scattering which causes changes in the magnetoresistance occurs depending on the angular difference between the magnetization directions in the second ferromagnetic film of the pinned magnetic layer and the free magnetic layer. Hence from the standpoint of obtaining a larger relative magnetoresistance change, it is desirable that the electrical resistance arising from other causes such as impurities and film defects, that is, the resistivity of the second ferromagnetic film, the free magnetic layer and the nonmagnetic layer, be small. To this end, in addition to the Nixe2x80x94Fe alloy which is generally used in the pinned magnetic layer of the aforementioned ferromagnetic film, Co, Coxe2x80x94Fe alloy, and other ferromagnetic materials are adopted, as described in the aforementioned laid-open patent application Hei7-169026 and elsewhere.
However, the resistivity of Co and Coxe2x80x94Fe alloy is approximately 15 xcexcxcexa9-cm, lower than NiFe. Hence it is easier for a sense current to flow in the first ferromagnetic film neighboring the antiferromagnetic layer; and so there is the problem that, under the influence of this shunting action the relative magnetoresistive change is reduced, lowering the sensitivity of the sensor.
A spin-valve magnetoresistance sensor is disclosed. In one embodiment, the spin-valve magnetoresistance sensor includes a free magnetic layer and a pinned magnetic layer. The pinned magnetic layer includes first and second ferromagnetic films formed in layers to enclose a nonmagnetic coupling film. The first ferromagnetic film is antiferromagnetically coupled to the second ferromagnetic film. The spin-valve magnetoresistance sensor also includes a nonmagnetic layer enclosed between the pinned and free magnetic layers and an antiferromagnetic layer neighboring the pinned magnetic layer. The antiferromagnetic layer is formed over a substrate. The first ferromagnetic film neighbors the antiferromagnetic layer and is formed of a high-resistivity Co-based material.